This invention is concerned with means for controlling flow instability in a centrifugal fluid compressor, such as an air compressor.
Flow instability is known to develop in centrifugal air compressors in the usual exhaust diffuser area after the flow has left the rotor and also in the rotor itself prior to leaving the rotor. The results of such instability is manifested by rotor oscillation, undesirable vibrations, noise, whistling, and surging or uneven air flow from the compressor. The present invention is directed to improving the stability of air flow through the compressor so as to not only eliminate these faults, but also to improve the overall efficiency of the compressor.
In accordance with the present invention, there is provided in a centrifugal fluid compressor including a first stage of compression comprising a rotor having an inducer inlet, a volute diffuser connected to the discharge end of the rotor, and a primary inlet passage; and a second stage of compression comprising a second rotor having an outlet line connected with its discharge end, and an inlet line connecting with the discharge end of the volute diffuser; a loop conduit means for recirculating fluid of compression from the outlet line of the second stage of compression when flow through the compressor drops below a predetermined level simultaneously to the primary inlet passage upstream of the inducer inlet of the rotor of the first stage of compression and to the volute diffuser of the first stage.